This disclosure relates in general to dual scale vehicle gauges and, more specifically, to a back lit dual scale vehicle gauge that selectively illuminates a first scale or a second scale.
Instrument panels 1 in vehicles traditionally include mechanical indicators 2 movable relative to a fixed gauge overlay 3. For example, a speedometer typically includes an indicator needle rotatably movable relative to a fixed gauge overlay. The overlay includes a plurality of numeric characters that define a scale 4 along the path of travel of the indicator that represent the speed of the vehicle. Most overlays include a miles per hour scale and a kilometers per hour scale. Typically, one of the scales is a primary scale with larger numeric characters and the other scale is a secondary scale with smaller numeric characters. FIG. 1B illustrates an overlay having a primary miles per hour scale and a secondary kilometers per hour scale. FIG. 2B illustrates an overlay having a primary kilometers per hour scale and a secondary miles per hour scale.
In the past, vehicle manufacturers stocked two different speedometers. The only difference between the speedometers was the scale defined on the overlay. An overlay with a primary miles per hour scale is used in speedometers for vehicles that are sold in countries that use the British measurement system. An overlay with a primary kilometers per hour scale is used in speedometers for vehicles that are sold in countries that use the metric measurement system. Most vehicle manufacturers produce vehicles that will be sold in countries that use the British measurement system and vehicles that will be sold in countries that use the metric measurement system. For example, a manufacturer of over the highway trucks and tractors may produce vehicles that will be sold in the United States and Canada. The vehicles sold in the United States will have speedometers with a miles per hour primary scale, while the vehicles sold in Canada will have speedometers with a kilometers per hour primary scale.
Digital reconfigurable displays have been developed that allow different gauges to be displayed with one display. These displays use a digital graphic representation of the traditional indicator and overlay. One reconfigurable display uses a transparent electroluminescent display to display different scales with a mechanical indicator positioned behind the display. The digital reconfigurable displays permit the user to select different gauges to be displayed, such as speed, battery, oil pressure, etc. Some digital reconfigurable displays allow the user to toggle between an miles per hour mode where a miles per hour scale is displayed and a kilometers per hour mode where a kilometers per hour scale is displayed.
One major drawback of digital reconfigurable displays is that the graphic representation of the gauge is unsatisfactory unless an expensive high resolution display is used. The pixels of a digital display do not define numeric characters that are as xe2x80x9ccrispxe2x80x9d or well defined as the characters stenciled into an overlay of an analog display. In addition, sun glare has a greater effect on digital displays than traditional analog displays.
There is a need for a back lit, dual scale, analog vehicle gauge that selectively illuminates a first scale or a second scale. Such a display eliminates the need for vehicle manufacturers to stock different speedometers having different overlays, is less expensive than digital reconfigurable displays and overcomes the deficiencies inherent in digital reconfigurable displays.
The present disclosure is directed to a dual scale gauge for a motor vehicle. The gauge includes a mechanical indicator, an overlay, a first light source, and a second light source. The mechanical indicator moves in response to a sensed condition of the motor vehicle. The overlay is positioned behind the mechanical indicator. The overlay includes first and second scales. The first and second scales are only visible when illuminated from a back side of the overlay. A first light source is positioned behind the overlay that illuminates the first scale and does not illuminate the second scale when the gauge is operated in a first mode. A second light source is positioned behind the overlay that illuminates the second scale and does not illuminate the first scale when the gauge is operated in a second mode.
In one embodiment, the first light source includes a lamp and a light guide positioned behind the first scale that directs light from the lamp to illuminate the first scale. The second light source also includes a lamp and a light guide. The second light guide is positioned behind the second scale and directs light from the second lamp to illuminate the second scale.
In one embodiment, the first light source includes a plurality of light emitting diodes positioned behind characters of the first scale to illuminate the characters of the first scale. The second light source comprises a second plurality of light emitting diodes positioned behind characters of the second scale for illuminating characters of the second scale.
An operator may select a first mode or a second mode. Light is provided by the first light source to illuminate the first scale, but not illuminate the second scale when the first mode is selected by the user. Light is provided by the second light source to illuminate the second scale and not the first scale when the second mode is selected.
In one embodiment, the dual scale gauge is a speedometer for a motor vehicle. In this embodiment, the overlay includes a kilometers per hour scale and a miles per hour scale. The kilometers per hour and miles per hour scales are only visible when illuminated from the backside of the overlay. The first light source is used to illuminate the miles per hour scale and the second light source is used to illuminate the kilometers per hour scale.
Additional features of the invention will become apparent and a fuller understanding will be obtained by reading the following detailed description in connection with the accompanying drawings.